At the time of European contact in the 16th and 17th centuries, the historic Calusa were the people of the Caloosahatchee culture. They are notable for having developed a complex culture based on estuarine fisheries rather than agriculture. Calusa territory reached from Charlotte Harbor to Cape Sable, all of present-day Charlotte and Lee counties, and may have included the Florida Keys at times. They had the highest population density of South Florida; estimates of total population at the time of European contact range from 10,000 to several times that, but these are speculative.
Calusa political influence and control also extended over other tribes in southern Florida, including the Mayaimi around Lake Okeechobee, and the Tequesta and Jaega on the southeast coast of the peninsula. Calusa influence may have also extended to the Ais tribe on the central east coast of Florida.
Early Spanish and French sources referred to the tribe, its chief town, and its chief as Calos, Calus, Caalus, and Carlos. Hernando de Escalante Fontaneda, a Spaniard held captive by the Calusa in the 16th century, recorded that Calusa meant "fierce people" in their language. By the early 19th century, Anglo-Americans in the area used the term Calusa for the people. It is based on the Creek and Mikasuki (languages of the present-day Seminole and Miccosukee nations) ethnonym for the people who had lived around the Caloosahatchee River (also from the Creek language).
Juan Rogel, a Jesuit missionary to the Calusa in the late 1560s, noted the chief's name as Carlos but wrote that the name of the "kingdom" was Escampaba, with an alternate spelling of Escampaha. Rogel also stated that the chief's name was Caalus, and that the Spanish had changed it to Carlos. Marquardt quotes a statement from the 1570s that "the Bay of Carlos ... in the Indian language is called Escampaba, for the cacique of this town, who afterward called himself Carlos in devotion to the Emperor" (Charles V, Holy Roman Emperor). Escampaba may be related to a place named Stapaba, which was identified in the area on an early 16th-century map.
Paleo-Indians entered what is now Florida at least 12,000 years ago. By around 5000 BC, people started living in villages near wetlands. Favored sites were likely occupied for multiple generations. Florida's climate had reached current conditions and the sea had risen close to its present level by about 3000 BC. People commonly occupied both fresh and saltwater wetlands. Because of their reliance on shellfish, they accumulated large shell middens during this period. Many people lived in large villages with purpose-built earthwork mounds, such as those at Horr's Island. People began creating fired pottery in Florida by 2000 BC.